■ Stomach

Although the stomach is not part of a routine transabdominal ultrasound study, except for some special cases, it quite often produces typical findings that have to be interpreted correctly. This calls not only for a systematic analysis of the above criteria but also for the use of a

5 MHz probe, which will improve the diagnostic interpretation (differentiation of the wall layers).

Assessment of any sonographic findings at the stomach has to consider quite precisely the time of the patient’s last ingestion. Interpreta-

tion may be facilitated and improved by oral fluid intake (with an antifoaming agent added). Specific sonomorphologic analysis of the gastric wall requires endoscopic/bioptic and endosonographic procedures.

Polypoid changes of the gastric wall are purely incidental findings and are best visualized with the stomach containing only very little fluid (Fig. 7.2). The polyp will appear as a sessile focal mass protruding into the gastric lumen and presenting as an atypical (off-center) pathological gut signature. Polyps arise from certain layers of the gastric wall, most often the mucosa and submucosa, but may also involve the deeper layers of the wall. A more precise analysis of the wall layers would require the use of high-frequency probes or

even endoscopic/endosonographic procedures. In larger polyps, color flow Doppler imaging may be able to demonstrate the intravascular blood flow. Polyps do not affect the outer delineation of the gastric gut signature. Being subjected to the peristaltic movement of the stomach wall, the sessile polyp will move passively and thus can be better differentiated from the mucosal folds. Since ultrasound cannot distinguish between benign and malignant polyps, it is impossible to differentiate a benign polyp from gastric adenocarcinoma type I.

Stromal Tumor

Gastrointestinal stromal tumors (GIST) are rare tumors of mesenchymal origin. They are normally related to a layer of the gastointestinal wall, but can also occur beyond the gastrointestinal wall and without a connection to it (eGIST). The most common location is the gas-

tric wall (ca. 60% occurrence). These tumors have smooth margins, are found in the layered wall of the stomach, quite often relate to one of the central layers, and are well vascularized. They exhibit interstitial growth and may reach a size of several centimeters (0.5–40 cm). Pos-

sible malignancy increases with size. Although these firm, elastic tumors display a somewhat varied echogenicity, they are mostly hypoechoic. In large tumors central necrosis can be detected (Figs. 7.3, 7.4, 7.5).

Focal adenocarcinoma may arise anywhere within the stomach (Table 7.3). Frequently, sonography will demonstrate a pathological concentric gut signature limited to the gastric antrum or cardia, while focal pathological atypical (off-center) gut signatures are more common in the corpus and rare in the fundus of the stomach. The typical lesion is visualized as a pathological thickening of the gastric wall with loss of the usual layering. Quite often the lesion is poorly delineated at the gastric lumen, and in case of concentric tumors it is not uncommon to encounter a stenotic lumen; in such cases there will be retention of food proximal to the stenosis. The immediate vicinity of the tumor shows a characteristic loss of peristalsis, while the pathological gut signature is hard and not compliant. The surface of the tumor may either be smooth or irregular. In advanced gastric carcinoma, there may be free fluid as well as lymphadenopathy around the pancreas, the porta hepatis, and/or the celiac axis (Figs. 7.6, 7.7, 7.8).

Fig. 7.6 Pathological gut signature with eccentric loss of wall layering, irregular and clearly thickened wall, ill-de- fined inner margin, and narrowed lumen.

Lymphoma

Gastric lymphoma may be visible on ultrasound as a focal hypoechoic mass involving the wall of the stomach, with clearly evident hypervascularity and loss of its typical layered appearance.

Gastric Varices

Varices of the gastric wall are quite common in portal hypertension; owing to their tortuous course, sectional views of these varices will appear as small anechoic/hypoechoic cystoid structures on the outside of the gastric wall (Fig. 7.9). At the gastric fundus and cardia, as well as at the distal esophagus, they may protrude transmurally into the lumen of the stomach as esophageal or fundic varices. Color flow Doppler scanning will demonstrate a ribbonlike hepatofugal portovenous blood flow.

Fig. 7.9 Gastric varices. Endosonography demonstrating varices in the gastric wall in portal hypertension.